Detecting and Treating Lung Congestion with Kidney Failure

Abstract

Fluid overload is a common complication in patients with CKD, particularly patients with kidney failure, a population with a very high risk for pulmonary edema. Lung ultrasound is now a well-validated technique that allows for reliable estimates of lung water in clinical practice. Several studies in patients with kidney failure documented a high prevalence of asymptomatic lung congestion of moderate to severe degree in this population, and this alteration was only weakly related with fluid excess as measured by bioimpedance spectroscopy. Furthermore, in these studies, lung congestion correlated in a dose-dependent fashion with death risk. In the Lung Water by Ultra-Sound Guided Treatment to Prevent Death and Cardiovascular Complications in High Risk Kidney Failure Patients with Cardiomyopathy (LUST) trial, a treatment strategy guided by lung ultrasound safely relieved lung congestion but failed to significantly reduce the risk for a combined end point including death, nonfatal myocardial infarction, and decompensated heart failure. However, in line with three trials in patients with heart failure, a post hoc analysis of the LUST trial showed that the use of lung ultrasound reduces the risk for repeated episodes of acute heart failure and repeated cardiovascular events. Given the high cardiovascular risk of pulmonary edema in patients with predialysis CKD, defining the epidemiology of lung congestion in this population is a public health priority. Specific trials in this population and additional trials in patients with kidney failure will establish whether targeting lung congestion at an asymptomatic phase may improve the severe cardiovascular prognosis of both patients predialysis and patients on dialysis.

Keywords: arteries; arteriosclerosis; blood pressure; cardiovascular; cardiovascular disease.

Figure 1.

The lung is a special territory where hydrostatic pressure has a peculiar regulation (53). Net filtration pressure at the alveolar level is zero or negative, which protects the lung from the risk of pulmonary edema in volume expansion states like CKD and heart failure. The peculiar microhemodynamic setting of the lung is guaranteed by a constant flow of lymphatic fluid from the pulmonary interstitium to the systemic circulation. Moreover, the lung also has a uniquely high interstitial compliance (54) like in nephrotic syndrome (55), a condition characterized by low oncotic pressure. Oncotic and osmotic forces facilitate the transfer of water from the interstitium to the systemic circulation and vice versa. Systemic inflammation increases the permeability of the alveolocapillary barrier and precipitates pulmonary edema, like in AKI pulmonary (56).

Figure 2.

Lung ultrasound (US) A and B lines. (Left panel) Normal lung US A lines (i.e., horizontal artifacts parallel to the pleural line indicating a normal lung surface are evident). (Right panel) In the presence of excess extravascular lung water, the subpleural interlobular septa thickened by edema reflect the US beam. This phenomenon generates reverberation artifacts (“comet tails”) called B lines, which are the US equivalent of B lines on chest x-rays. These lines move with the pleural line when this moves. Detailed definition criteria for US B lines are reported in ref. .

Figure 3.

Twenty-eight sites and 4 sites lung US scores. The first well-standardized US method for quantifying lung water was on the basis of recordings made at 28 precise points in the intercostal spaces (upper panel) (58). Shorter methods taking 1 minute or less focus on eight (59) or just four points (60). The four sites score measures the number of US B lines in the third intercostal space in two areas per side of the thorax (lower panel). These methods apply different scores but provide substantially similar information (61,62). Automated software on the basis of artificial intelligence has already been implemented in some commercially available machines and may allow operator-independent quantification of lung water.

Figure 4.

Trend of US B lines in the active and control groups. (A) Data are means and 95% confidence intervals (95% CIs). (B) Data (means and 95% CIs) are data fitted by the linear mixed model (LMM). Reprinted from ref. , with permission.